The present invention relates generally to membrane-type separation and fractionation apparatus for separating and collecting a desired component from a whole fluid, and more specifically to a pressure monitoring system for monitoring trans-membrane pressure in such apparatus.
Microporous membrane filter devices have come into wide use in selective separation and purification procedures, such as hemodialysis and plasmapheresis, for separating a desired fluid component from a continuously flowing whole fluid. Typically, such filter devices are incorporated in a disposable flow system, which is installed in a processing apparatus during the procedure, and then disposed of after a single use.
In a preferred form the filter devices take the form of a bundle of parallel microporous hollow fibers arranged side-by-side in the form of a bundle within a hollow cylindrical housing. As the whole fluid is caused to flow through the fibers the desired fluid component passes through the walls of the fiber membrane to the surrounding container, which forms a collection chamber from which the separated component is transported to a collection device. A preferred construction and method of manufacture of such a hollow fiber filter is shown in the copending application of Robert Lee and William J. Schnell, entitled, "Microporous Hollow Fiber Membrane Assembly and Its Method of Manufacture", Ser. No. 278,913, filed June 29, 1981. A preferred apparatus for use with such a hollow fiber filter is shown in the copending applications of Arnold C. Bilstad et al; entitled, "Blood Fractionation Apparatus", Ser. No. 330,898; entitled, "Blood Fractionation Apparatus having Collected Volume Display", Ser. No. 330,899; entitled, "Blood Fractionation Apparatus have Collection Rate Display", Ser. No. 330,901; and entitled, "Blood Fractionation Apparatus having Replacement Fluid Rate Control System", Ser. No. 330,900, all filed Dec. 15, 1981, and assigned to the present assignee.
In microporous membrane devices the walls of the membrane have pores which are permeable to air and other gases, thereby permitting air and gases to readily pass through. However, notwithstanding their air-permeable nature, the walls retain a semi-permeable or permselective characteristic and serve to restrict the flow of a liquid passing through them, as in blood oxygenators, or to restrict the flow of a component of the liquid passing through, such as blood cells in membrane plasmapheresis devices. Materials from which a microporous hollow fiber filter element can be made include thermal plastic polymers, such as polypropylene. These polymers can be formed into hollow fibers by known processes such as solution or melt spinning.
The efficient operation of membrane-type filter devices, particularly hollow-fiber type devices in continuous flow plasmapheresis apparatus, requires that the pressure differential between the supply and collection sides of the hollow fiber membrane, termed trans-membrane pressure (TMP), be monitored and maintained within predetermined operational limits.
A preferred equalizer valve apparatus and method for adjusting TMP pressure in a hollow fiber filler system is shown in the copending applications of Clinton Kopp et al; entitled, "Membrane Plasmapheresis Apparatus and Procedure", Ser. No. 277,428; entitled, "Fluid Flow Control Device", Ser. No. 277,449; and entitled, "Fluid Flow Control Device", Ser. No. 277,414; all filed June 25, 1981 and assigned to the present assignee.
Allowing the TMP pressure to become too high in any portion of the filter may result in undesired blood components, such as RED blood cells, restricting or clogging the membrane, or may cause red blood cells to rupture or lyse as they flow through the filter assembly. Allowing the TMP pressure to be too low may result in inefficient operation of the filter, since the desired component does not readily flow through the filter membrane. Accordingly, it is desirable that continuous flow filter-type separation and fractionation apparatus include a system for monitoring trans-membrane pressure.
One requirement of any trans-membrane pressure monitoring system is that it provide a continuous output reading, preferably in digital form, which can be quickly and easily interpreted by an operator of the apparatus. Furthermore, the system must not interfere with the operation of the apparatus or the associated disposable flow system, and must not compromise the sterility of the flow system or allow bacterial contamination of the apparatus or the surrounding environment by the fluid being processed. The present invention is directed to a monitoring system which meets these requirements by providing in a plasmapheresis apparatus or the like a continuous digital readout of TMP without compromise to the operation or bacterial isolation of the associated flow system.
The TMP monitoring system of the present invention may be constructed to read TMP between the whole blood inlet and the plasma outlet of a hollow fiber membrane filter, as shown in the illustrated embodiment, thereby displaying the maximum TMP present in the filter, or may be constructed to read whole blood pressure at one or more alternate locations, or, at both the whole blood inlet and outlet, to display the average TMP in the filter.
In a preferred form of the TMP monitoring system of the present invention disposable pressure transducer isolators are provided to prevent bacterial contamination. These isolators, which comprise a microporous synthetic polymer barrier having sufficient porosity to allow passage of gas, but insufficient porosity to prevent passage of bacteria, are constructed in accordance with the teachings of the copending application of Arnold C. Bilstad et al, entitled "Pressure Transducer Isolator and Method", Ser. No. 353,546, filed Mar. 1, 1982. In addition to providing isolation between the disposable fluid flow system and the pressure transducers, these pressure isolators provide integration or modulation of pressure variations in the system to prevent such variations from affecting the TMP readings developed by the monitoring system. Moreover, these isolators are relatively low in cost and sterilizable by conventional sterilization techniques, making their inclusion in disposable flow systems feasible.
Accordingly, one of the principal objects of the present invention is to provide a new and improved trans-membrane pressure monitoring system for use in conjunction with a filter device in a fluid separator or fractionation apparatus, such as utilized for hemodialysis and plasmapheresis.
Another principal object of the invention is to provide a trans-membrane pressure monitoring system for use in plasmapheresis apparatus and the like which does not interfere with the operation of the apparatus and which provides a continuous easily readable display of trans-membrane pressure.
Another principal object of the invention is to provide a trans-membrane pressure monitoring system for use in plasmapheresis apparatus or the like which is not subject to contamination by bacteria or microorganisms in fluid being processed.